It is known to produce brominated styrenic polymers by brominating a styrenic polymer in a suitable solvent using bromine or bromine chloride and an antimony trihalide catalyst. See in this connection U.S. Pat. No. 4,352,909 to Barda et al., and U.S. Pat. No. 5,723,549 to Dever et al., the full disclosures of which are incorporated herein by reference. One of the products made in this way is a commercially available product available under the trademark Pyro-Chek 68PB flame retardant.
In order to minimize contamination of the brominated styrenic polymer product by excessive amounts of antimony catalyst residues, it has been the practice to subject the bromination reaction mass to an aqueous work up and to precipitate the antimony catalyst residues from the aqueous phase first as the oxychloride and then as the sulfide. In order to operate the process on a more efficient cost-effectiveness basis, it is desired to recover as much of the antimony catalyst residues as possible on an economical basis and if feasible, to recover the residues in a form that can be recycled for use as catalyst in the bromination step. It would be especially advantageous if the recovered product could be reused as catalyst in the process without adversely affecting either the bromination reaction or the properties of the brominated flame retardant product formed therewith.
This invention is deemed to achieve most, if not all, of these desired objectives.